Satellite antenna array with electrically adjustable beam shaping



March 10, 1970 HANS-DIETRICH KUHNE ETAL 3,500,418

1 SATELLITE ANTENNA ARRAY WITH ELECTRICALLY ADJUSTABLE BEAM SHAPINGFiled Aug. 29. 1966 3 Sheets-Sheet l Fig.7

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Inventors:

United States Patent 1 Claim ABSTRACT OF THE DISCLOSURE An antenna arrayis mounted on a satellite so as to direct the signals toward the earthin a uniform field. Each antenna in the array is angularly mounted withrespect to the otherand has an electrically variable dielectric meansmounted at the aperture. The means are electrically adjustable by acommon control system to shape the beam. I

The present invention relates to an antenna system for anearthsatellite.

As is Well known, artificial communication satellites have recently beenput into orbit around the earth. of the many possible tracks which suchearth satellites can follow, the circular orbits are of particularinterest, irrespective of whether the communication system uses oneearth satellite, a plurality of earth satellites, or a socalled twentyJ-four hour or synchronous satellite which appears to stand still overone point on the earth. In such systems, the'duration of one period,i.e., one orbit around the earth, the position of the satellite on thetrack, and the circular configuration of the track have to be maintainedwitha certain amount of accuracy. If the satellite occupies a givenposition with respect-to the earth, this has a greaf' -deal of influenceon the expense and elab- Orateness of the communication efifiipmentcarried aboard the satellite, inasmuch as a satellite which occupies agiven position with respect to the farth can utilize directionalantennas. 1

Assuming that the main axis of the radiation pattern continuously pointsto the center of the-'earth, the electric field strength obtained at theedges of he surface portion of the earth which is visible from thesatellite will be weaker inasmuch as the distance between a point nearthe center of the earths surface portion; seen from the satellite andthe satellite is less than the distance between a point in the region ofthe edge of this...surface portion of the earth and the satellite.Furthermore, the radiation patterns of antennas which were up to nowused in satellite antennas are generally lobe-shaped, and this alsocontributes to a decreased field strength in the region of the edges ofthat surface portion of the earth which is visible from the satellite.The amount of the decrease depends primarily on the directivity of theparticular antenna system being used.

It will be appreciated that the above conditions are undesirable, and itis the primary object of the present invention to provide a way in whichto eliminate the disadvantages of existing antenna systems used insatellites.

With the above objective in view, the present invention residesbasically in an antenna system for an earth satellite having adirectivity characteristic or radiation pattern which produces, over aslarge a portion of the earths surface as possible, the same electricfield strength and as low an electric field strength as possible outsideof such portion of the earths surface. In accordance with the presentinvention, the antenna system comprises an array of antennas, whoseapertures preferably lie in the same plane, and which are so dimensionedand arranged,

3,500,418 Patented Mar. 10, 1970 and/or the phases of whose fieldstrengths are so influenced, as to obtain the desired radiation pattern.

Additional objects and advantages of the present invention willbecom'e'a'pparent upon consideration of the following description' whentaken in conjunction with the accompanying drawings in which:

FIGURE 1 shows the optimal radiation pattern of an antenna arrayaccording to the present invention.

FIGURE 2 shows the radiation pattern of conventional satellite antennas.

FIGURE 3 shows two antennas whose axes are inclined with respect to eachother.

FIGURE 4 is 'an end view of a four-antenna array according to thepresent invention.

FIGURE 5 shows an array of five antennas fed by a common feed.

FIGURE 6 shows an array of three antennas two of which are provided withphase shifting elements.

FIGURE 7 shows how the characteristic of a phase shifting element may bevaried.

FIGURE 8 shows a metallized plastic antenna element.

FIGURE 9 shows in more detail the structure of the antennas of FIGURE 3and the phase shifting arrangement used with these antennas.

Referring now to the drawings, FIGURE 1 shows the optimal directionalcharacteristic of a satellite antenna, this being a characteristic whichcauses the electric field strength of the received field to be constantover a predetermined portion of the earths surface, in particular, asurface portion which subtends an angle a so that the radiation whichstrikes each point in this surface portion will be of the same fieldstrength. By way of comparison, FIGURE 2 shows the directionalcharacteristic of heretofore conventional satellite antenna systems.

In accordancewith one embodiment of the present invention, the desireddIrectional characteristic is obtained by positioning the individualradiators obliquely with respect to each other, Thus, as shown in FIGURE3, multi-horn-type antennas are so arranged that their axes form anangle 1E? with each other which depends on the height of the satellite.

An array incorporating a plurality of individual reflectors makes itpossible to use circularly polarized waves. Such an array is sit iown inFIGURE 4 which depicts four horns whose apertures lie in a common planeand together form a square. Here, too, the axes of the horns may bearranged obliquely with respect to each other. It will be understood, ofcourse, that the array according to the present invention is not limitedfor use with circular y polarized waves in that differently polarizedwaves can be used.

In the embodiment of FIGURE 5, the antenna array comprises a pluralityof dipoles D which are fed from a common feed S, there being interposedbetween the feed and the individual dipoles respective phase shifters Pby means of which the phases of the individual antennas can beinfluenced. Feeding of the individual antennas will be chosen in amanner disclosed in our copending application Serial No. 575,669 filedAugust 29, 1966 for getting the desired lobe that means an oscillatoryenergy distribution with a maximum in the middle of the aperture and adecreasing amplitude towards the edge of the aperture. This means thatan antenna arrangement from which FIG. 5 shows a side view consists ofseveral circlelike zones the resulting phase of each changes by suitablechoosing the phase shifters P.

A part of the array shown in FIGURE 6 comprises three individualparabolic reflectors which together form a common aperture area. Inorder to achieve the desired phase shift, elements E made of metallic ordielectric material are arranged in the vicinity of the apertureopenings of the two outer antennas.

In the embodiment of FIGURE 7, there is shown how the dielectricconstant and/or the permeability constant of a dielectric phase shiftingelement such as is shown at E in FIGURE 6 can be varied by applying apredetermined field, so that the phase can be shifted by varying thevoltage which is put out by a voltage source U and applied across thedielectric element. In this way, any undesired change in position of thesatellite, or change in the configuration of the orbit, can becompensated for. Such compensation can also be made if any given areawithin the portion of the earths surface illuminated by the array is,for any reason, to be excluded.

FIGURE 8 shows one antenna consisting, mainly, of plastic material F,the same being provided with a metallized coating M. In this way, thetotal weight of the antenna system is kept to a minimum which, it willbe appreciated, is of considerable importance in the case of an antennasystem that is to be carried aboard a satellite.

FIGURE 9 shows the variable dielectric phase shifting arrangement asdisclosed in FIGURE 7 and the metallized plastic antenna structure asdisclosed in FIGURE 8 applied to the antenna array as in FIGURE 3. Eachof the antennas is formed of plastic material having a metallizedcoating. The aperture of each antenna has a phase shifting element Earranged in front of it. A variable voltage source V is connected acrosseach of the elements B, so as to vary the dielectric thereof. Each ofthe variable voltage sources V is electrically connected to a phaseshifter P, which in turn is connected to the common feed S.

It will thus be seen that, in accordance with the present invention,there is provided an antenna system in which the desired radiationpattern, namely, a radiation pattern that produces, over as large aportion of the earths surface as possible, the same electric fieldstrength and as low an electric field strength as possible outside ofsuch portion of the earths surface, is obtained by means of an antennasystem which comprises an array of a plurality of individual antennasand means associated with these antennas for causing the array as awhole to produce the desired radiation pattern. That is to say, thedesired radiation pattern is achieved by so dimensioning and arrangingthe individual antennas, and/or by so influencing the phases of thefield strengths of the antennas, as to obtain the desired radiationpattern.

It is also pointed out that if the spin of the satellite is stabilized,the desired radiation pattern can be approximated by making theradiation pattern rotationally symmetrical with respect to the spinaxis. This, however, means that most of the energy is radiated indirections which will result in most of the energy being lost, i.e., innot being picked up by the receiving stations on the earths surface. Inorder to avoid this, at least certain parts of the antenna system can beso influenced that energy is directed only toward a desired region onthe earths surface. This can be done, as explained above, byelectrically or mechanically switching the antennas, or by suitablycontrolling the phase of the energy coming in through the feed line.

The antennas themselves may be in the form of horns, spirals,longitudinal reflectors, or dipoles.

It will be understood that the above description of the presentinvention is susceptible to various modifications, changes, andadaptations, and the same are intended to be comprehended within themeaning and range of equivalents of the appended claim.

What is claimed is:

1. An antenna system comprising a satellite, a plurality of individualantennas mounted on the satellite, said antennas having their axesarranged at an angle with respect to each other whereby the antennasradiate signals in different directions, phase shifting means forvarying the phase of the signal of each antenna comprising a variabledielectric element mounted in front of each antenna and means forvarying the dielectric constant of each dielectric element to therebyvary the phase of the associated antenna signal.

References Cited UNITED STATES PATENTS 2,286,839 6/1942 Schelkunolf343853 2,432,990 12/1947 Hansen 343-778 3,184,743 5/1965 Crawford343-778 3,188,640 6/1965 Simon et al. 343-705 3,259,902 7/1966 Malech343-754 3,339,275 9/1967 Anderson et al 343-786 ELI LIEBERMAN, PrimaryExaminer U.S. Cl. X.R. 343-754, 854

